Constitutively Active Notch4 Receptor Promotes Flow-Induced Arterial Outward Remodeling

Notch is expressed in arterial but not venous endothelial cells (ECs). Notch signaling plays a critical role during vascular development and is required for postnatal arterial remodeling following ischemic injury. However, whether activated Notch is sufficient to promote arterial remodeling is unclear. Shear stress is a primary stimulus for arterial outward remodeling, and shear stress induces Notch activation. We hypothesized that activated Notch in turn promotes flow-induced arterial outward remodeling. Constitutively active Notch4 (Notch4*) was expressed in arterial ECs of the carotid artery to bypass hemodynamic perturbations caused by pan-endothelial Notch4 activation. First, we used an artery graft model: a segment of the carotid from a Notch4* donor was grafted into a control recipient. Notch4* expression was restricted to ECs of the graft; hemodynamics in the control recipient was not perturbed. Second, we targeted Notch4* expression using the arterial EC-specific Bmx(PAC)-CreER T2 . The carotid ligation model was used to examine flow-induced outward remodeling. Histological analysis showed that in high-flow Notch4* artery grafts, external elastic lamina (EEL) circumference, EEL area, medial area, and medial thickness were larger compared to controls. In high-flow Bmx-Notch4* arteries, internal elastic lamina circumference, EEL circumference, EEL area, and medial area were larger compared to controls. To bolster our findings in the carotid, we tested our hypothesis using a mesenteric artery ligation model. Post-ligation, shear stress in high-flow Notch4* and control mesenteric arteries were comparable. While high-flow arteries in both Notch4* mutants and controls were enlarged, radial enlargement was increased in Notch4* arteries compared with controls. Together, our results showed that endothelial expression of Notch4* enhanced flow-induced outward remodeling of both the large-diameter, elastic carotid artery and the small-diameter, muscular mesenteric artery. Notably, in the absence of increased flow, basal arterial diameters were comparable between Notch4* and control mice. These data suggest that, when properly targeted to the arterial endothelium, Notch4* promotes flow-induced outward remodeling.